1. Field of the Invention
The present invention relates to simple or multiple semi-reflective metallized glass sheets and their process of manufacture by means of vacuum evaporation, comprising an improved alloy anchoring layer.
2. Prior Art
It is known that the term semi-reflective glasses or glazings refers to glass (or other transparent material) sheets comprising a coating upon the glass surface of one or more layers of a metal, a metallic alloy or a metal compound of sufficient thinness so as to at least partially transmit visible light and at the same time to be of such a nature that it also reflects the major portion of infrared radiation that is incident upon it. These glazings have the advantage that in the summer they are transparent to visible radiation of sun rays while reflecting the incoming infrared radiation and in the winter they reflect back the outward transmission of radiation coming from within the building.
While a great many types of semi-reflective glazings have been proposed in the past, those most widely used today are glasses which generally comprise three superimposed elemental layers, namely (1) an anchoring layer that is in contact with the surface of the glass and whose main function is to provide an excellent adherence and a good support structure for the layers that are superimposed upon it; (2) an intermediate layer or semi-reflective layer whose function is to impart to the glass the main desired optical characteristics; and (3) a protective surface layer or dielectric layer whose main function is to permit one to adjust to the desired values the extent of the transmission of the visible spectrum and the extent of the reflection of the infrared radiation. For example, the anchoring layer may consist of nickel and chromium; the intermediate layer is usually comprised of gold, silver or copper; and the protective surface layer is generally comprised of a dielectric material such as silicon oxide SiO, zinc sulfide or a mixed indium and tin oxide. It is also possible to interpose a dielectric layer beneath the reflective layer.
Nickel-chromium anchoring layers are generally deposited by means of vacuum evaporation from evaporation crucibles which are themselves constructed of a very refractory metal such as, for instances, tungsten. It has been observed that the process of vacuum evaporation of said component alloy materials for such an anchoring layer, which must be performed at a temperature of about 1500.degree. C., causes the evaporation crucibles to be severely corroded, and frequently to be broken, thus giving inadmissible irregularities of the layer and of its properties. It is thus apparent that the use of these prior art processes on an industrial scale for the manufacture of large-sized semi-reflective glasses leads to an inordinately high cost.
This invention is directed to such multi-layered semi-reflective glasses as discussed above. More particularly, the present invention is directed to semi-reflective glasses and their process of manufacture comprising an improved alloy anchoring layer exhibiting great advantages in comparison with the semi-reflective glasses and processes of the prior art.